1. Field of the Invention
The present invention relates to a lighting unit for a vehicle in which a light distribution pattern for a low beam (lower beam) and a light distribution pattern for a high beam (upper beam) can be switched freely.
2. Related Art
Conventionally, some vehicle lighting devices such as headlamps have a structure in which a light distribution pattern for a low beam and a light distribution pattern for a high beam can be switched freely. For example, there has been known a vehicle lighting device of a four-lamp type in which low and high beams are constituted by an LED and a bulb, respectively.
In the vehicle lighting device of the multi-lamp type, however, it is hard to considerably reduce a size of the lighting device.
In a lighting device of a projector type which is provided with a projection lens disposed on an optical axis extended in a longitudinal direction of the vehicle and a reflector disposed behind the projection lens, particularly, a plurality of projection lenses and reflectors are provided side by side.
For this reason, a size of a whole lighting device is enlarged.
In order to reduce the size, JP-U-63-111704 discloses a headlamp of a projector type in which a light source bulb is disposed in a vicinity of a first focal point of a reflecting mirror (reflector). A light emitted from the light source bulb is reflected by the reflecting mirror. A second focal point of the reflecting mirror is positioned in a vicinity of a member having a cut line (a cutoff line forming member).
The reflected light is irradiated forward by a convex lens.
In the head lamp, a plane mirror is provided in the cutoff line forming member to increase a quantity of a light and is tilted to switch into a high beam.
Moreover, in a lighting device disclosed in JP-A-2006-164735 or JP-A-2005-108554, an additional light source for a high beam is provided. In the lighting device, there is provided a lighting unit of a projector type having two types of light distributing functions by a projection lens disposed on an optical axis extended in a longitudinal direction of the vehicle and first and second light source units disposed behind the projection lens. A light distribution pattern for a low beam having a clear cutoff line on an upper end of the light distribution pattern is formed by turning on the first light source unit, and an additional light distribution pattern for a high beam which is expanded upward from the cutoff line is added to form a light distribution pattern for a high beam by additionally turning on the second light source unit.
However, in the headlamp of a projector type disclosed in JP-U-63-111704, a bulb is used as a light source. Therefore, it is necessary to maintain a size in the reflector to some degree and it is hard to reduce a size of the lighting device.
Moreover, when the cutoff line forming member provided on the plane mirror is tilted to form a light distribution pattern for a high beam, it is impossible to increase a quantity of a light by the plane mirror. Consequently, a maximum quantity of the light is decreased so that a performance of the high beam cannot be satisfied. In the case in which an LED is used for a light source in order to reduce the size of the lighting device, an insufficient quantity of the light in the high beam becomes more remarkable.
On the other hand, the headlamp disclosed in JP-A-2006-164735 or JP-A-2005-108554, it is possible to reduce a size by using the LED as the light source and to increase the quantity of a light to some degree by additionally turning on the second light source unit. However, a tip of a shade for a low beam is fixed on a rear focal point of a lens. For this reason, a part of a beam irradiated by additionally turning on the second light source unit (the additional light source) generates an eclipse by the tip of the shade, and a center of the light distribution pattern for a high beam does not completely overlap with the light distribution pattern for a low beam.
In the light distribution pattern for a high beam, therefore, it is impossible to form a strong light collecting pattern in an overlap with the light distribution pattern for a low beam without an incompatibility (a dark portion generated by the eclipse). In order to effectively utilize the beam of the second light source unit, moreover, it is necessary to cause the additional light source to collect a light in the vicinity of the rear focal point. With the structure, however, alight generating the eclipse by the tip of the shade is increased so that a loss is increased.